1. Field of the Invention
The present invention relates generally large freight containers used in intermodal freight transportation systems, in which the freight containers are stacked upon each other and transported by truck, rail, ship, and combinations thereof. In particular, the present invention relates to a freight container having an improved lift casting that are compatible with existing lift mechanisms and existing freight containers.
2. Description of Related Art
Large freight containers used in intermodal freight transportation systems are well known in the art. The intermodal freight transportation industry has always been very competitive. As with most competitive industries, any technological innovation that provides a competitive advantage is highly sought after. Thus, there is an ever-present need for faster, better, safer, and cheaper methods of transporting goods, both domestically and internationally.
In an effort to achieve maximum strength at minimum weight, these large freight containers are typically made of steel frames and aluminum skins. Load-bearing steel reinforcement beams are integrated into the exterior of the container in the walls, ceiling, and floor at certain industry-recognized locations along the lengths of the containers. These reinforcement beams provide the necessary strength to allow the freight containers to be lifted and stacked on top of each other. The reinforcement beams are comprised of side posts integrated into the container walls, headers integrated into the container ceilings, and footers integrated into the container floors. The headers are connected to the side posts at “lift” castings. The footers are connected to the side posts at “stack” castings. Unfortunately, due to height restrictions and strength requirements, lift castings and stack castings must protrude into the interior of the container. This intrusion not only reduces the available storage volume of the container, but makes it difficult to load the container, as well. Operators must maneuver cargo around these intrusions to prevent damaging the cargo or the castings. This is costly both in the amount of cargo that can be shipped, and in the additional time required to load a container.
Individual lift castings and stack castings usually have apertures on both their tops and their sides that allow the container to be lifted by conventional lift mechanisms, or cranes. The lift mechanisms lift, move, and stack the containers on top of each other between the different modes of transportation. These lift mechanisms have hydraulically actuated arms and lift attachments that are adapted to spread to the appropriate width and attach to the container through either the side apertures or the top apertures in the lift castings. The apertures in the stack castings are aligned with the apertures in the lift castings so that the containers can be coupled together by standard inter-box connectors (“IBC's”).
Over the years, the desire to pack increased volumes of freight into a container has led to an evolutionary increase in the length and width of freight containers. Due to certain height restrictions in the transportation of containers over land and rail, such has the clearance height of bridges and tunnels, the overall height of the containers has generally remained unchanged. However, containers have increased from a length of 40′ and width of 96″ to lengths as long as 53′ and widths as wide as 102″. Although larger containers are able to hold a greater volume of freight, significant structural problems arise when larger containers are used in conjunction with smaller containers in the overall intermodal transportation system.
For example, when all of the containers in an intermodal transportation system are of the same size, one container can be stacked on top of other containers, and the reinforcement beams of the containers remain aligned. Thus, the load of the upper container is transmitted through the stack casting of the upper container, through the inter-box connector, through the lift casting of the lower container and down to the stack casting of the lower container to the stacking surface. On the other hand, when larger containers are used with smaller containers, the reinforcement beams and castings of the larger container do not align with the reinforcement beams and castings of the smaller container. This offset creates undesirable bending moments and bending stresses in the reinforcement beams and castings of both containers, thereby causing the reinforcement beams and castings on the containers to buckle and fail under the bending loads. In addition, because prolonged vibration of stacked containers in intermodal transportation often leads to fatigue failure of the reinforcement beams, constant and expensive container maintenance and inspection programs are required.
A number of efforts have been made to alleviate this problem. For example, intrusive support braces have been added to the lift castings, additional reinforcement plates have been added to the exterior of the containers adjacent to the lift castings, and additional mounting apertures have been added to the stack castings. Some containers have lift castings that do not allow other containers to be stacked on top of the container at all.
With these increases in container size, it has been necessary to modify the design of lift castings and stack castings, as well. However, due to the long life of these freight containers, and the large number of older containers currently in service, it is inevitable that new containers will be used in intermodal transportation systems with existing containers. Thus, it is desirable that newly designed containers include lift castings and stack castings that align with the lift castings and stack castings of older containers, thereby making new containers backward compatible with older containers.
Despite the above-mentioned advances in the art, there is a need for an improved freight container for use in intermodal freight transportation systems that has lift castings in which a top lift aperture is located at an outboard position, so that when other containers are stacked on top of the improved container, the load is properly distributed through reinforcement beams of the improved container.
There is also a need for an improved lift casting for use on freight containers, the improved lift casting having a top lift aperture that is located at an outboard position.
In addition, there is a need for an improved bayonet-type twist lock mechanism for use on freight container lift mechanisms, the bayonet-type twist lock having a shorter tapered point that extends into the lift casting a shorter distance than existing bayonet-type twist locks.
Also, there is a need for an improved method of lifting and transporting freight containers.